Method of Making Monolithic Concrete Structures

ABSTRACT

A method of making a monolithic portion of a concrete building from a combination of pre-cast and cast-in-situ elements distributes moments and shear loads by using flanged pre-cast columns for support. In addition, a precast ‘waffle’ element is used to reduce the overall weight of the slab being formed. In preferred versions of this method support arms are provided that link formwork to an anchor cast into a pre-cast column and from the anchor to a load bearing point on a lower, pre-cured slab.

RELATION TO OTHER APPLICATIONS

This application is a continuation-in-part of the inventor'sPCT/EG2006/000032, filed on Aug. 24, 2006 and designating the UnitedStates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to concrete building units that may comprise bothpre-cast and cast-in-situ portions to provide a continuous cementitiousstructure that distributes loads and moments so that less concrete isneeded.

2. Background Information

In U.S. Pat. No. 7,121,061, the inventor teaches a method for making amonolithic reinforced concrete portion of a building by first erectingflanged wall members in a facing relationship, where at least one flangeon each wall member preferably extends horizontally toward a facing wallmember by about 10-25% of the intramural spacing. A slab extendingacross the intramural spacing is either cast in situ or formed bygrouting a precast slab element into place. An advantage of this methodis that when a complete room is defined by the wall elements, the methoddistributes moments and shear in two dimensions and thereby allows forthe use of lighter, thinner structural elements. A disadvantage of thismethod is that its reliance on laterally extensive prefabricated wallmembers restricts its use to structures, such as apartment dwellings,that have relatively small openings in those wall modules, and precludesits use for structures, such as garages, warehouses and industrialbuildings, that commonly provide relatively large open spaces by usingspaced apart columns to support a ceiling or roof.

In DE 2,251,613, Schmidt teaches a method of fabricating a multi-storeycementitious structure in which spaced-apart columns support theabove-grade levels. Schmidt's columns are pre-fabricated with flangesextending laterally by nearly one half of the inter-column spacing. Arow of such columns is erected and the flanges on adjacent columns aregrouted together to define a horizontal beam. Pre-fabricated concreteplanks are then laid between two parallel beams and the planks aregrouted together and to the beams so as to form a monolithic structure.A disadvantage of Schmidt's method is that the load imposed by theconcrete planks is distributed one dimensionally, rather than in bothlateral dimensions. This requires the beams and columns to be heavierand stronger than would be the case if the loads and moments weredistributed in two dimensions.

In U.S. Pat. No. 1,516,074 Borg teaches a method of making a monolithicconcrete structure in which a plurality of slabs is supported by anotherplurality of columns. Borg does not teach providing two dimensionalsupport of horizontally extensive portions of his structure while thestructure is being grouted together.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is that it provides a method of making amonolithic reinforced concrete upper slab portion of a buildingsupported by four or more precast columns. The columns are generallyerected above a lower slab to define one or more generally rectangularbays having a respective column at each of its corners. Moreover, eachof the precast columns has a reinforced rigid flange portion extendingout horizontally at the selected height from the upper slab. Each flangeportion, which is preferably square in a plan view, has rebar cast intoit and extending outward from portions of all four of its edges. Thecolumns are oriented so that each flange portion has two edges parallelto and facing respective edges of the flange portions of two othercolumns so as to define four rectangular border areas, each of whichextends between a respective pair of the flange portions. A temporarysupport is placed in the middle of the bay defined by a set of fourcolumns and a rectangular precast central slab preferably having rebarextending outward from all four edges is placed on it. The dimensions ofthe central slab are chosen so that the slab covers most of the bay andabuts, or slightly overlaps, all four border areas and the respectivecorner portions of all four associated columns. Formwork supported fromthe lower slab is placed beneath the border areas and concrete is pouredto form the desired monolithic slab portion comprising the central slaband all four flange portions. This system distributes the loads andmoments to all four sides, rather than only two sides, thus allowing forthinner slabs, which reduces weight, materials costs and labor.

In a preferred embodiment of the method, each of the precast columnscomprises an anchor that is preferably a metal member cast into thecolumn at a height about half way between the lower and upper slabs.When columns of this sort are provided, the formwork deployed beneaththe border areas may be supported during casting by means of supportarms connected to these anchors. In a preferred embodiment, each anchoris directly connected to two support arms, one of which extends from theanchor outward and upward to the formwork and the other of which extendsfrom the anchor outward and downward to a load bearing point on thelower slab.

Another aspect of the invention is that it provides a method of using arelatively low weight slab member for making a monolithic reinforcedconcrete portion of a building comprising a monolithic slab supported bya plurality of columns. These columns are preferably erected at the fourcorners of one or more rectangular bays. The low weight slab or slabsare then placed atop the columns and are cemented thereto. The lowweight slab members comprise a plurality of reinforced beam portionsextending parallel to each of the edges of the slab member and an arrayof low-density regions disposed intermediate the beam portions. Rebarpreferably extends along each reinforced beam portion and protrudesoutwardly from each end thereof.

In a preferred embodiment, the slab member is formed by setting therebar in position in a mold that defines the beam portions, placingblocks of polymeric foam in the regions between the rows of rebar andthen casting the slab member. In particularly preferred cases, theweight is further reduced by providing that much of the precast slabmember is thinner than the final slab. This minimizes the weight ofprecast pieces that need to be lifted and lowered into position andallows the builder to bring the entire slab up to a final specifiedthickness by pouring additional concrete on top of the pre-cast slabmember.

In a particular preferred embodiment, the slab member comprises steppedor rabbeted edges in which an upper portion of the edge region extendsall the way to the edge of the slab member and the lower portion of theedge region is stepped back therefrom. When used with a column having acomplementary rabbeted flange in which a lower portion protrudes fartherthan an upper one, each corner of the slab can be placed in abuttingcontact with a respective flange prior to cementing the slab member tothe column.

Although it is believed that the foregoing rather broad summarydescription may be of use to one who is skilled in the art and whowishes to learn how to practice the invention, it will be recognizedthat the foregoing recital is not intended to list all of the featuresand advantages. Those skilled in the art will appreciate that they mayreadily use both the underlying ideas and the specific embodimentsdisclosed in the following Detailed Description as a basis for designingother arrangements for carrying out the same purposes of the presentinvention and that such equivalent constructions are within the spiritand scope of the invention in its broadest form. Moreover, it may benoted that different embodiments of the invention may provide variouscombinations of the recited features and advantages of the invention,and that less than all of the recited features and advantages may beprovided by some embodiments.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic perspective view of an intermediate step informing a slab.

FIG. 2 is a cross-sectional view of an upper portion of a flangedcolumn, the section taken as indicated by the arrow 2-2 in FIG. 1.

FIG. 3 is a detail view, as indicated by the phantom circle 3 in FIG. 1,the view showing a corner of a column flange disposed beneath a cornerof a central slab member.

FIG. 4 is a plan view of a preferred central slab.

FIG. 5 a is a cross section of a central slab having raised beamsections, the section taken as indicated by the arrow 5 a,b-5 a,b inFIG. 4.

FIG. 5 b is a cross section of a preferred central slab having somerebar held in place with stirrups, the section taken as indicated by thedouble-headed arrow 5 a,b-5 a,b in FIG. 4.

FIG. 6 a is another cross section of the slab of FIG. 5 a, the sectiontaken as indicated by the arrow 6 a,b-6 a,b in FIG. 4.

FIG. 6 b is another cross section of the preferred central slab, thesection taken as indicated by the arrow 6 a,b-6 a,b in FIG. 4.

FIG. 7 is a sectional view showing temporary support arms used tosupport formwork used in casting a border area, the section taken asindicated by the arrow 7-7 in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In studying this Detailed Description, the reader may be aided by notingthe definitions of certain words and phrases used throughout this patentdocument. Wherever those definitions are provided, those of ordinaryskill in the art should understand that in many, if not most instances,such definitions apply to both preceding and following uses of suchdefined words and phrases. At the outset of this Description, one maynote that the terms “include” and “comprise,” as well as derivativesthereof, mean inclusion without limitation; the term “or,” is inclusive,meaning and/or. The term “bay”, as used herein, stands for a rectangularhorizontal division of a structure, and in particular stands for aregion defined by a rectangular grid that may have a column at eachcorner thereof or that may have columns at two corners and a wallportion along one side. The term “rebar” is used herein to denoteelongated reinforcing members of any sort and includes, but is notlimited to, steel reinforcing bars.

Turning now to FIG. 1, one finds a schematic depiction of anintermediate step in a process of forming a slab 10 by joining aplurality of flange portions 12 of respective columns 14 with a centralprecast slab portion 16 and by casting border areas 18, which extendoutward from the bay 20, in situ. Although the drawing depicts only asingle bay 20, the reader will understand that the process hereindescribed is applicable to a multi-bay arrangement. Moreover, althoughthe depicted single bay has a column at each corner, the reader shouldrecognize that flanged wall members, as described by the inventor in hisU.S. Pat. No. 7,121,061 can be substituted for pairs of the depictedcolumns. The disclosure of U.S. Pat. No. 7,121,061 is fully incorporatedherein by reference.

In a preferred configuration, such as that shown in FIG. 2, each column14 comprises both a vertically extensive portion 22 and a flangedportion 12 that preferably comprises a stepped or rabbeted edge region24 in which a lower portion 26 of the edge region extends furtheroutward from the vertically extensive portion 22 than does an upperportion 28. This rabbeted edge arrangement is similar to that used onwall members described in the inventor's U.S. Pat. No. 7,121,061, andhas the same preferred height ratios, set-back distances and protrusionlengths for rebar 29. The rabbeted arrangement aids in transferringshear loads from a supported portion of the slab to the rigid flange,and thence to the vertically extensive portion of all of the columns andto neighboring bays. In a particular preferred embodiment the lowerportion of the rabbet extends ten to twenty centimeters outward beyondthe upper portion of the rabbet. In order to provide a desirable overlaparrangement with a central slab member 16, rebar does not protrude fromthe corners 30 of the flange portions.

Although the columns 14 are depicted in the drawing as having a flat topsurface, which accords with a process of making a single storey abovegrade, the reader should realize that many other arrangements arepossible and that, more generally, the top of each column may compriseattachment means for mounting the base of another column used to supporta yet higher storey in the structure.

The preferred central slab 16 has a complementary rabbeted edge regionin which an upper portion of the edge region 32 extends further outwardthan does a lower portion 34. This allows each corner 35 of the slabmember 16 to rest upon a respective corner of a column flange 12, asdepicted in FIG. 3. As described above with respect to the flangeportions, although the central slab member preferably has rebarextending outward from all its edges, there is no rebar extendingoutward from the corner portions that overlap with the flange portions.

Turning now to FIG. 4, one finds a plan view of a preferred central slabmember, which is configured as a “waffle”. The preferred central slabmember comprises a rim portion 36 having the rabbet edge featuresdescribed above. In addition, the slab 16 comprises a grid of reinforcedbeam portions 38 running parallel to the edges of the slab 16. The upperportion of the beam portions 38 may have rebar cast into them, asdepicted in FIGS. 5 a and 6 a. Preferably, the reinforced beam portionscomprise rebar cast into lower portions of the beam and other rebar heldon top of the beam portions by means of stirrups 39. The rebar retainedin stirrups is preferably cast into the center section during a singleconcrete pour that tops off the waffle section and forms the border areaportions of the slab. Rebar preferably protrudes through and outwardfrom the ends of these beam portions as depicted in FIGS. 5 a,b and 6a,b. The areas between the beam portions are preferably only about halfthe maximum thickness of the central slab member 16, and may be filled,at least partially, with foamed plastic blocks 40 or other lightweightitems.

In a preferred process, the central slab 16 is pre-cast using foamedplastic blocks 40 having outwardly protruding ears or lugs 42. Duringthis casting operation, the blocks 40 are held in position by the mold(not shown). Subsequently, when concrete is cast on top of the foam, aswill be hereinafter described, the lugs 42 prevent the heavy concreteabove the blocks from pushing the blocks out through the bottom of theprecast slab 16. The reader will recognize that other means of lockingthe low density blocks into the concrete may also be employed and thatthese include, without limitation, providing a recessed region in thefoam and inserting rebar through the foam and into adjacent areas priorto casting.

In a preferred process the columns 14 and wall members (not shown) areerected on a hardened bottom slab 44 or are supported above a bottomslab by being attached to another column or wall at a lower level in thestructure—i.e., a column or wall associated with a building storey belowthe bottom slab. Free-standing temporary supports 46 are then placed inthe central portion of each bay and respective central slab members areplaced onto each one of them. As described above, in preferredarrangements, corners of the slabs are supported not only by thetemporary support 46, but also by the corners of respective columnflanges, as depicted in FIG. 3.

After the central slab members are in place, the preferred process callsfor the erection of formwork 47 in the border areas. At this pointadditional rebar 29 may be introduced into the border areas andpreferably fastened to rebar protruding from a slab or flange byclamping, welding, or by any other known means. In a preferred processthe formwork in the border areas is supported by a combination oftemporary trusses 48 and support arms 50. In this arrangement a firstsupport arm 50 is fastened between a truss 48 and a respective anchor 52in a column adjacent to the truss, as depicted in FIG. 7. Each suchcolumn may then be connected to a load bearing point 54 on the bottomslab 44. This arrangement has several advantages, not the least of whichis that it provides more open space for movement of people and equipmenton the bottom slab during the process of setting up for the concretepour.

The preferred process allows for a single concrete pour to complete theslab by filling in the forms in the border areas and by also filling inthose portions of the central slabs that have a reduced thickness.

Although the present invention has been described with respect toseveral preferred embodiments, many modifications and alterations can bemade without departing from the invention. Accordingly, it is intendedthat all such modifications and alterations be considered as within thespirit and scope of the invention as defined in the attached claims.

1) A method of making a monolithic reinforced concrete portion of abuilding comprising an upper slab portion having a selected thicknessextending between a top surface at a selected top height to a bottomsurface at a selected bottom height, the slab portion connected to fourcolumns defining a rectangular bay, the method comprising the steps of:a) providing the four precast reinforced columns respectively erected atrespective corners of the rectangular bay, each of the columnscomprising a respective vertically extensive portion and a respectivehorizontally extensive rectangular reinforced rigid flange portionhaving rebar protruding from each of its four edges, wherein each of theflange members has a top surface at the selected top height, the columnsoriented so that each flange portion has two edges parallel to andfacing respective edges of two other of the flange portions so as todefine four border areas, each of which extends between a respectivepair of the flange portions; b) placing a first temporary support withinthe rectangular bay so that a top of the support is substantially at theselected bottom height; c) placing a rectangular reinforced precastcentral slab member on the first support, the central slab memberextending across the bay so as to abut all four of the flange members,the central slab member having a thickness over most of its area that isless than the thickness of the upper slab portion, the central slabmember having rebar protruding outward from each of its edges; d)supporting respective forms beneath each of the border areas; e) pouringconcrete over the forms and the central slab member to form the upperslab portion; f) waiting for the concrete to harden; and g) removing thesupports. 2) The method of claim 1 wherein each of the flange portionscomprises four rabbeted edge portions, each of which comprises arespective lower portion extending further away from the associatedcolumn portion than does a respective upper portion, wherein both theupper and lower portions have rebar extending outwardly therefrom. 3)The method of claim 1 wherein the central slab comprises four rabbetededge portions, each of which comprises a respective upper portionextending to a respective edge of the central slab and a respectivelower portion that does not extend to the respective edge, wherein boththe upper and lower portions have rebar extending outwardly therefrom.4) The method of claim 1 wherein: each of the flange portions comprisesfour rabbeted edge portions, each of which comprises a respective lowerportion extending further away from the associated column portion thandoes a respective upper portion, and wherein both the upper and lowerportions have rebar extending outwardly therefrom except in four flangecorner regions; each of the central slab portions comprises fourrabbeted edge portions, each of which comprises a respective upperportion extending to a respective edge of the central slab and arespective lower portion that does not extend to the respective edge,wherein both the upper and lower portions have rebar extending outwardlytherefrom except in four central slab corner regions; and wherein thedimensions of the flange portions and central slab are selected so thatwhen the central slab is placed on the first temporary support, each ofthe four central slab corner regions rests on top of a respective flangeportion corner region. 5) The method of claim 1 comprising an additionalstep, carried out before the concrete is poured, of placing additionalrebar in each of the border areas, the additional rebar running parallelto a nearest central slab edge. 6) The method of claim 1 wherein each ofthe columns comprises a respective anchor disposed in the verticallyextensive portion thereof, and wherein the step of supporting arespective form plate beneath each of the border areas comprisesconnecting a respective first support arm between the respective formplate and the anchor disposed in a respective one of the pair of columnsdefining the respective border area; and connecting a respective secondsupport arm between each of the respective anchors and a cured bottomslab. 7) The method of claim 1 wherein the central slab comprises twomutually perpendicular sets of rebar running between respective paralleledges thereof, the slab further comprising a plurality of low densityelements. 8) A method of making a monolithic reinforced concrete portionof a building comprising an upper slab supported by a plurality ofcolumns extending above a bottom slab, the method comprising the stepsof: a) providing the plurality of precast reinforced columns comprisingrespective vertically extensive portions and respective horizontallyextensive rigid flange portions disposed at a selected slab height,wherein each vertically extensive portion comprises a respective anchorfor connecting a support arm to the column; b) erecting the columns toextend from a lower slab to at least the height of the upper slab; c)placing formwork extending between at least two of the columns andsupporting the formwork by a combination of at least two first and atleast two second support arms, wherein each of the first support armsconnects a respective portion of the formwork to a respective anchor andwherein each second support arm connects the respective anchor to arespective load bearing point on the bottom slab; d) pouring concreteonto the formwork and allowing it to harden; and e) removing the supportarms and the formwork. 9) The method of claim 8 wherein each anchorcomprises a respective metal member cast into a respective column. 10)The method of claim 8 wherein each support arm is adjustable in length.11) A method of making a monolithic reinforced concrete portion of abuilding comprising a slab supported by a plurality of columnscomprising at least four columns erected at the four corners of arectangular bay, the method comprising the steps of: a) providing arectangular pre-cast slab member comprising a plurality of reinforcedbeam portions extending parallel to each of the edges of the slab memberand an array of low-density regions disposed intermediate the beamportions, the slab member comprising rebar extending outward from eachof the beam portions along each of the four edges of the slab member; b)supporting the slab member in abutting contact with each of the columns;and c) pouring concrete to join the slab member to the columns. 12) Themethod of claim 11 wherein the low density regions comprise polymericfoam blocks having protrusions extending outward from faces thereof. 13)The method of claim 11 wherein each of the columns comprises a laterallyextensive flange portion having a rabbeted edge in which an upperportion of the flange portion is stepped back from the edge; wherein theslab member comprises a rabbeted edge in which a lower portion of theslab member is stepped back from the edge and wherein the step ofsupporting the slab member in abutting contract comprises placing eachof four corner portions of the slab member on respective corner portionsof each of the flange portions. 14) The method of claim 11 whereinselected portions of the slab member have a thickness equal to thethickness of the slab and other selected portions of the slab memberhave a thickness substantially equal to one half of the slab thickness.